The present invention generally relates to an antenna device. More specifically, the present invention relates to an antenna device particularly for mobile radio telephone devices. The present invention is further directed to a mobile radio telephone device.
It is standard in mobile radio telephone devices to employ what are referred to as tuned or matched antennas, i.e. antennas whose effective length has a specific relationship to the wavelength .lambda. of the frequency range to be received. Given a mobile radio telephone device for what is referred to as the GSM standard, the frequency range to be received/transmitted amounts to approximately 900 MHZ through 1000 MHZ. Accordingly, the wavelength of this frequency range lies at approximately thirty through thirty-five cm.
An antenna that is tuned to half the wavelength of the frequency range to be received must thus exhibit an effective electrical length of about fifteen through eighteen cm for the GSM standard. It is obvious that an antenna having a length of 15-18 cm is a great disadvantage given the desire to make a mobile radio telephone device as handy as possible. A firmly attached antenna of this size projecting from the housing of the mobile radio telephone device is also out of the question for the reason that such an antenna is an extreme risk in view of damage by bending or breaking.
Up to now, it has been standard to provide a mobile radio telephone device with a rod antenna of the aforementioned length that can be telescoped in or to provide a helix antenna (spiral antenna) having the same electrical length or to provide a combination of helix and rod antenna. Before the mobile radio telephone device is placed in operation, the antenna must be pulled out in the case of a rod antenna. This solution has the disadvantage that the transmission/reception power of the mobile radio telephone device is deteriorated when the operator forgets to pull the antenna out before operation of the mobile radio telephone device. A helix antenna by itself has the disadvantage of poor reception/transmission properties, i.e. poor performance.